Process of depositing metals on metallic surfaces and the product thereof.



.1 v UN E STATES PATENT IoE.

sggn RD looWPEa-coLEs, or LONDON, ENGLAND, ASSIGNOR, BYaIEsNE I AssIeNME Ts'ToTnE SHERARDIZING sYNDIoATE, LIMITED, OF WEST- MINSTER, LoNDomENeLAN A CORPORATION or GREAT BRITAIN.

PROCESS OF D EPOSlTlNG METALS ON MEI-Arne SURFACES AND THE PRODUCT THEREOFQ- SPECIFICATION forming part of Letters Patent No. "701,298, dated June 3, 1902.

' Application filed my 24,1901. :SerialNo. 69,587. on specimens.)

To ctZZ whom it may concern.-

Be it known that I, SHEEAR'D COWPER- CoLEs, electrometallurgist, of 46 Mor'peth Mansions, Morpeth Terrace, WVestminster, London, England, have invented certain new and usefullmprovements in the Process of 1 Depositing a Metal on Metallic Surfaces and the Product Thereof, of which the following is a specification.

This invention relates to a process of depositing zipc or equivalent metal on iron or having its surface coated with such deposit.

By this method the iron or steel acted on has formed on it a thin homogeneous covering of j zine, rendering it non-corrodibl.

Hitherto the most successful results with I regard to the deposition ofzinc on iron or 5 ically, generally known as the cold gal steel have been achievedeither by dipping the metal to be coated in a bath of molten zinc, usually known as the hot galvanizingmethod, or depositing the zinc electrolytvanizing method. In the former case there are two principal disadvantagesnamely,the

difficulty of regulating the depth and even distribution of the deposit and the deleterious effect of the heat of the bath on the metal be ing coated. Inthe case of the electrolytic process the deposition can be better regulated and thetemper of the metal is unaffected, so that this latter process is undoubtedly well adapted for certain articles, such as tubes;

- but is not easily applicable to large masses of meta1,sucl1 as castings, or to'articles of intricate form. I I r By my process thethickness and evenness of the deposit can be regulated as desired,

and any description or shape of iron or steel can be satisfactorily and economically dealt with.

but this invention is not limited to these metals. For example, zinc may be deposited on brass or copper, or a zinc alloy maybe used in place of zinc alone.

The surfaces of the articles to be coated are preferably first cleansed by any well-known process, such as pickling or by the sand-blast, and are then placed in a metal-receptacle; preferably of iron or steel, and covered with zinc-dust. The air should be excluded as much as possible, and for this reason a closed receptacle is generally preferable. This receptacle or box is then submitted to the action of heat (about the dull-red heat of iron is sufficient) for half an hour to an hour, depending on the thickness of deposit required. This receptacle is then allowed to cool and the articles Withdrawn, when they will be found to have deposited on their surfaces a smooth tough adherent coating of zinc. The remainder of zinc dust employed may be used again, and if the air has been excluded, as previously referred to, the loss of efficiency is very small. Under certain circumstances We may use a higher temperature, which ap pears to cause the deposit to penetrate more deeply.

What is commercially known as zincdust contains some oxid of zinc-about ten per cent..

If metallic zinc in the form of powder or pulverulent zinc is employed, a certain proportion of the oxid of zinc must be present to produce the result. This can be efiected by adding oxid of zinc or submitting the metallic zinc to oxidizing influences.

It is Well known that zinc-dust will not melt at high'temperatures; but I have discovered a method of obtaining a' deposit of metallic zinc from it, as described.

In some cases a small percentage of carbon (by Way of example three per cent.) intimately mixed with the zinc-dust results in a IOO results. The temperature and the amount of carbon can be varied, the above example being merely typical. A convenient way of doing this is mixing a little hydrocarbon, such as Vaseline or grease, with the zinc-dust, as this makes the application in certain cases more easy and economical.

The deposit on the iron or steel can be formed of more or less thickness, according to the length of time during which the zincdust is allowed to act on it. If the zinc deposit so formed be removed by any mechanical means, such as filing or chipping, the surface of the iron exposed is still unaffected by corrosion.

This invention will be found very useful for protecting the surface of silver and the like from the effects of corrosive agencies, such as sulfureted hydrogen. The silver or other metal is subjected to the same process as that already described in the case of iron or steel.

The utility of the process as applied to silver is that a film of zinc is deposited on the surface of the silver, and so prevents the silver being affected by the sulfur and other impuritiesin the atmosphere, and so tarnishing.

Metallic surfaces covered with zinc according to this invention have the following characteristics: The deposit of zinc is homogeneous and in this respect is difierent from hot galvanizing. In appearance it also differs from galvanized iron or steel, and this difference of appearance is due to difference of structure. In the case of this invention the zinc deposit appears to be free from crystalline formation. Moreover, the application of the process has the effect of imparting a delicate silver-gray tint to the article treated. Under the microscope enlarging to fifty diameters the difference between samples made according to this process and those made according to ordinary galvanizing processes is very marked both in structure and formation. In the latter case the coating is distinctly crystalline and in the former it is apparently not so.

What I claim, and desire to secure by Letters Patent, is

1. The process of depositing zinc on metallic surfaces which process consists in applying to the metallic surface pulverulent zinc partially oxidized and in submitting the same to heat.

lic surfaces which process consists in apply;

ing to the metallic surface what is known in commerce as zinc-dust and in submitting the same to heat.

5. The process of depositing zinc on iron surfaces which process consists in applying to the iron surface zinc-dust and in submitting the same to heat.

6. The process of depositing zinc on metallic surfaces which process consists in applying to the metallic surface pulverulent zinc containing not less than eight per cent. zinc oxid and in submitting the same to heat.

7. The process of depositing zinc on metallic surfaces which process consists in applying to the metallic surface pulverulent zinc containing not less than eight per cent. zinc oxid and in submitting the same to heat in a closed chamber.

8. The process of depositing zinc on metallic surfaces which process consists in applying to the metallic surface pulverulent zinc containing not less than eight per cent. zinc oxid and submitting the same to heat in the presence of a small percentage of carbon.

9. As a new product a metallic object with its surface covered with zinc having the following characteristics, a homogeneous coating of zinc, having a physical connection with the metal underneath, and having the appearance to the naked eye of a delicate silver gray and not shiny like galvanized articles and having the distinguishing appearance under the microscope of homogeneous particles free from crystalline structure.

In witness whereof I have hereunto signed my name in the presence of two subscribing WVitnesses:

ROBERT W. SPEARPOINT, JOHN D. VENN. 

